Transformer protective switch



Dec. 8, 1953 s. R. SMITH, JR

TRANSFORMER PROTECTIVE SWITCH Filed Feb. l5, 1952 Inventor Sidneg R.Smith HIS Atto-Teg Fi g4.

Patented Dec. 8, 1953 .TaANsFoRMEa PROTECTIVE sWIToH Sidney R. Smith,Jr., Pittseld, Mass., assignor to General Electric Company, acorporation of New York Application February 15, 1952, Serial No.271,765

2 Claims.

This invention relates to a protective device for electrical apparatushaving high voltage and low voltage windings, such as a transformer, andmore particularly to means for interrupting the current flowing throughthe windings upon the occurrence of a predetermined condition of load onthe transformer.

Broadly speaking, various arrangements have been provided in the past toaccomplish this purpose. For example, a current responsive means such asa bimetallic element has been series connected in the secondary circuitto serve as an actuating means to separate a pair of interruptingcontacts series connected in the primary circuit. In some cases, thecurrent responsive actuating means as well as the interrupting contactshas also been series connected in the primary circuit. However, therehave been certain defects or objections to all such arrangements knownto applicant. Inasmuch as the actuating energy of the bimetallicelements, for example, usually has been transmitted more or lessdirectly from the bimetallic element to movable interrupting contactsand since the movement of a bimetallic element is relatively limited,the movement or separation of the interrupting contacts has likewisebeen limited or has been smaller than desirable to interrupt highvoltage currents. Moreover, the amount of energy available from bimetalsis relatively small and is not suflicient to actuate simple mechanicalcontacts in a reclosing manner with suflicient travel of the contacts torepeatedly interrupt the short circuit current of the transformer.Furthermore, in the event of permanent faults in the secondary circuit,the v elements therein continued to open and close the interruptingswitch in the primary an indefinite number of times until such time asthe fault was removed from the system. Such continual action,

of course, resulted in a relatively short life of the L tively fragileand, since it must be produced by specialists in the electronics eld, israther costly. For the same reason, the mechanical means usuallyemployed to interconnect the actuating element in the secondary with theinterrupting .switch in the primary, such as a snap acting (Cl. 20o-116)over-center togg1e, is relatively costly since it is very fussy to makeand assemble, and must be intimately tied in with the calibration of theswitch. Moreover, the trend in the power dis- -tribution field is tolarger transformer sizes, which imposes a heavier interrupting duty thansuch a vacuum type switch will handle.

It is therefore an object of this invention to provide a new andimproved circuit interrupting means.

It is also an object of this invention to provide an improved protectivearrangement for a transformer in connection with which the operation ofan interrupting switch in the primary circuit is controlled by a thermalmeans responsive to current in the secondary circuit, but is directlyand independently actuated by a separate drive means.

It is a further object of this invention to provide an interruptingswitch of the reclosing type, which will lock open following apredetermined number of openings and closings caused by a faultcondition in the secondary circuit.

It is also an object of this invention to provide a reclosing typeprotective switch for a transformer, together with a combinationindicating and resetting means to indicate, outside of the transformer,whether the switch is opened or closed and also permit resetting of thDswitch from the outside of the transformer.

The invention will be better understood from the following descriptionwhen taken with the accompanying drawing, and the scope of the inventionwill be pointed out in the appended .claims In the drawing, Fig. 1 is aside elevation view partly'in section of a transformer, generallyshowing the protective switch as positioned in relation to the windingstherein; Fig. 2 is an enlarged perspective view of the entire switchwith the exception of the main support base thereof and a cover orenclosure therefor; Fig, 3 is an end elevation view of the right-handportion of the device as illustrated in Fig". 2; Fig. Li shows thecombination resetting and indicator arm and the indicating dial thereforas viewed from the exterior of the transformer, and Fig. 5 is aschematic diagram illustrating the relationship of the switch to thetransformer windings and circuits therein.l

Referring now to Fig. 1, there is illustrated an dielectric I3, such asoil or a halogena-ted hydro-` carbon. @Immersed within the insulatingdielectric are the transformer core and windings generally designated bythe numeral I4.

The low voltage or secondary winding of transformer IU is provided witha mid-tap so that three secondary terminal leads, I5, I6 and I1 5 (seeFig. are provided, I6 forming the midtap and being usually grounded. Thetransformer casingk Il is `provided With'a .cover I8 which supports ahigh voltage bushing I9. Preferably mounted within high voltage bushingI9 y10 is a suitable protective device such as a bushing fuse 20, only aportion of which is yshown.; Bushing fuse provides protection to adistribution line 2| to which the high; voltage winding may be connectedas shown in-Fig.5,-and insures `15 'i continuity of service as far asthe distribution line is concerned by disconnectingthe Itrans-,- formerin the vent of an internal fault.

The circuit interrupting switch proper ofthe invention, best shown inFigs. 2 and 3, comprises 20 a lstationary contact- `22 .electricallyconnected 'to the transformer primary winding 23 as shown in.` Fig. 5and a relatively .movable switch'armr24 `of conducting materialf.electricallyl connected i toy ground. Contact 22 is mountedon asupportbase25I 25 of insulating material; shown onlyin fpart in Fig. 2 in theinterest. of simplicity.. Support base 25 `is fixed inrany suitablemanner vto 'theutransformercore I4 `so that aHtheelements of the deviceare immersed in the liquid die1ec-tricas30 illustrated. in Fig.Y 1.Switch arm` 241,r having a contact end26engageable withfixed contact 22a and anielongated-slot l21. adjacent-'the opposite end thereof, ispivotally-mounted intermediates the ends on a shaft 2B solasto`bevfreely rotatable 35 with respectthereto.'V Shaft :28 `is rotatablymounted in shaft supports 2I-and130yivhich`may be an integral part of orfixedly mounted on support base .1251." Switch arm 24pm-,electricallyconnected to a terminal 3| meuntedonl support base 40 25 by a conductor32 provided with sufficient slack to permit` free movementofswitcharrnf24r- The l terminal 3I= and thus the-switchrarm-is invturnelectrically connected'to ground as )by a vconductor 33 groundedtoithettransformer casing` at 34,?r 45 Fig. l1.

Although switch armA 24' iswcontrolled Ajor ,rene dered operative onlyin response `to a faultvconditionin the.secondarycircuitzor inresponse,to the temperature ofthefliquid dielectric I3 'in a.. manner which willbedescribed hereinafter, contacts 26 and 422'are positively :anddirectlywengaged andfdisengagedby an independentdrivemeansl comprisingadrivinggshaftf35 rotatably mounted in a support 36in turnnxedly mountedon support base 25,:eand. a drivenshaft'31 also rortatably mounted 4insupport-36, .support AStand an intermediate supportfiirlwhichr Ymaybefan'in- Y tegral part of or xedlymounted on support plate" or base '25mAftorsion or coiled spring 39-With 60 one end fixed to shaft35.and `theopposite end thereof xed to a pin Illle fixedlymountedfin the upwardlyextending arms-of=support 361serves as an energy source, whenwoundvlrelatively tight, to drives-haft 35' ina counterclockwisedirection 65 as viewed in Fig. `2. f As illustrated,` driving shaft 35extends to the exteriorv of `the transformer casing through astuffngbox,-not shown, or any other suitable means to prevent leakageofthe dielectric liquid I3`and is provided with-a com- 70 binationresettingand-'indicator arm 4I flxedly mounted on the exterior-end'thereof.' Shaft'35ll also extends throughfan-opening in anindicator dial42 mounted on the outer surface-ofthe cas-f` ing II. Driven-shaftfBlisdriven-in=ac1ockwise= 75 direction by driving shaft 35 at a higher speedthan shaft 35 by a pair of engageable spur gears 43 and 44 respectivelymounted on and fixed or keyed to shafts 35 and 31. A drive escapementdisk 45 having a tooth 46 in the periphery thereof is keyed or otherwisesuitably fixed to driven shaft 31 at the end thereof opposite to spurgear 44.v Disk 45 is provided with aswitch arm drive or crank pin 41which projects laterally from a face of the disk and extends throughslot 21 in switch arm 24 as illustrated. Crank pin 41 has a diameterslightly less than the width of slot opening 21 so that vit is freelyslidable therein and will cause. oscillation of switch arm 24 toalternately-disengage, then engage, etc. contacts 22 and 25 as disk 45is rotated clockwise by spring 39.,.as Willbemore clearly understood byinspection ofA Fig. 3.

However,-as previously pointed out, the rotation of the switch drivemeans including disk 45 and' `pin 41v is lcontrolled by zacurrentresponsive means in the secondary circuit of the transformer@` andcomprises ay pair -of bimetallic elements 46.

and49 electrically connected in series in secondaryl terminal leadsI5=.andI1 respectively as illustrated in-Fig.,5. Each bimetallic elementis-,f fixedly mounted to support base 25 at one end of I the element,`which endV is electrically `connected by a conductor I5'.or I1` to oneyend ofthe second-- ary winding 5l),` for example, while the oppositeend of each:bimetallicaelementis freely-movable andr electricallyconnected `lby a conductor vto a terminal which inturnisconnected by aleadito a f wall bushing terminal.` lor example; conductor I5 havingsufficient slacksoas not to impair the movement of the free endofbimetallic element 48 i electrically connects this `end of the elementwith a terminal 5 I; whichiinturn is connected by conductor I5 tosecondary wallbushingor terminal 52.1 The free fend cfleach bimetallcelement carriesfan adjustable screw v53, each engageable withI an arm54,preferablymade ofinsulating materialV and fixedly mounted at'oppositeends o rotatable shaft 28.- In addition-shaft y28 carries a 'drive brakemeans comprising a drive or escapement disk Aholding latch 55 :xedlymounted on the shaft and having afpair of arms 56 `and 51, the

endsof which-are' alternately fengageable with theftooth 46 :ondisk45qupon rotation of arms 54 respectively in opposite directions.-

Under-;normal currentyconditions in the ,loadfv circuit connected to.the transformer secondary winding, the free .end'ofeach bimetallicelement remains inv thexlowerfor yfull linexpositionillus-` AtratedinFig. 3,. with the arms54v biased into engagementv withthe -adjustableiscrews V53 fbyA a 1 spring 58, and Vwith the-.endfofxflatch armv 51: in;engagement'lwith toothlllti on :disk 45jV so.- thatV switch armcontact2will ,be maintained inengagement with stationary contact122'as`illustrated. However, upon theoccurrence of a pre-` determined` faultconditionsin the loe-.dccircuity thefree endof one or bothv'of the'bimetallic elements will be flexed upwardly',` whereupon the adjustablescrew lor screwswl` "will causeupward or counterclockwise rotationofarms 54, shaft 28,v and brake latch 55 to effect disengagement o1 latcharm 51y thereof from disktooth 46,"and permit torsion spring .33 tolefiectclockwise .ro-

tation of disk 45,'-counterclockwise rotation. of-

switch4 arm 24, and movement of Vthe disk-tooth'V latchfarm 56, therendof whichwas previously.

. moved into the path of the tooth travel. Engagement ofl arm 56 withtooth 4@ will maintain switch arm 24 in this position and the contacts224 and 2S out of engagement until such time as the cooling of thebimetallic elements caused by interruption of the current in the primarywinding results in flexing of the bimetallic elements downwardly to theillustrated full line position. Biasing spring 58 will, of course, causearms 54 to follow, causing clockwise rotation of latch 55 anddisengagement of latch arm 55 from tooth 4S, whereupon torsion spring 3swill effect engagement of contacts 22 and ES by rotating switch arm 24clockwise to the illustrated full line position. In the event that thefault in the secondary circuit was only temporary and has been removedin some manner, engagement or latch arm 5l with tooth 46 on disk d5 willmaintain the contacts in engagement. Ii, however, the fault ispermanent, the bimetallic elements will again be heated and flexedupwardly, causing further openings and reclosines of the switch in theprimary circuit in the manner described. However, following apredetermined number of such openings and closings, experience has shownthat the fault is probably a permanent one and, other than earlydestruction of the contacts and failure of the switch mechanism, nothingwill be accomplished by permitting the switch opening and closingoperations to continue. Thus, I have provided a stop pin 59 mounted onand projecting laterally from the face of the spur gear d3 a sumcientdistance so that, upon counterclockwise rotation of gear 42, it willeventually engage the vertical edge of one of the upstanding legs ofsupport 36 when contacts 22 and 25 have been separated, following thethird reclosing operation of the switch. Thus, further movement of theswitch drive will be prevented and the switch will be locked in the openposition to isolate the faulted load circuit from the balance of thedistribution system until such time as the fault has been removed. Theswitch may then be reset by turning the resetting and indicator arm c!in a clockwise direction until the pointed end thereto operate theswitch upon the occurrence of i.,

subsequent faults.

In addition to being responsive to a predetermined current in the loadcircuits, the thermal means comprising bimetallic elements it and 49 arealso responsive to the temperature of the transformer oil or liquiddielectric i3. Under certain conditions, even when the load current inthe secondary is of a relatively small value, the oil temperature mightbe excessively high either due to high ambient temperature or fromprevious loading or from both in which event the biinetallic elementswill be ilexed sufciently to effect disengagement of the contacts in theprimary circuit thus allowing maximum safe loading of the transformerunder all conditions.

Thus a transformer protective switch has been provided which iscontrolled in response to a fault in the secondary circuit but ispositively actuated by an independent drive means. lvloreover, I haveprovided a reclosing type transformer protective switch which willinterrupt the transformer primary circuit four times in case of apermanent fault, and then lock open until manually reset. Furthermore bythe employment of an independent switch drive driven by a spring 6means, sufcient energy is available for operating the interruptingcontacts without resorting to the more expensive vacuum type switchwhich is capable of interrupting an appreciable but nevertheless limitedamount of power with small movement of its contacts.

While I have, in accordance with the patent statutes, shown anddescribed a particular embodiment of my invention, it will be obviousthat changes and modifications can be made without departing from theinvention in its broader aspects and I, therefore, aim in the appendedclaims to cover all such changes and modifications that fall within thetrue spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A protective device for electric apparatus comprising a relativelystationary contact and a rotatably mounted switch arm, said switch armhaving a contact end engageable with said stationary contact and anelongated slot adjacent the opposite end thereof, switch drive meansmcluding a driving shaft and a driven shaft mounted in a supportstructure, said drive shaft having an indicator arm xedly mounted on anend thereof, a driving gear Xedly mounted on said driving shaft, adriven gear xedly mounted on driven shaft and engageable with saiddriving gear, an escapement disk having a single tooth in the peripherythereof xedly mounted en said driven shaft, a pin projectingtransversely from a face of said disk and engageable with said slot insaid switch arm, a torsion spring biasing said shafts, said indicatorarm and said escapement disk for rotation in one direction to causeoscillation of said switch arm and alternate disengagement andengagement of said contact end with said stationary contact, a driveholding latch xedly mounted for rotational movement on a shaft, a latchoperating arm idxedly mounted for rotational movement on said latchshaft, said drive holding latch having a pair of arms alternatelyengageable with said tooth upon rotation of said holding latch and saidoperating arm respectively in opposite directions, a bimetallic elementxedly mounted at one end and the opposite end of said element beingengageable with said latch operating arm and movable in response to afault condition in said electrical apparatus to cause disengagement ofone of said latch arms from said tooth to permit movement of said drivemeans and disengagement of said contacts and to simultaneously causemovement of the other of said arms for engagement with said tooth tolimit the movement of said drive means and maintain said contacts out ofengagement, and a spring biasing said latch operating arm for movementin a direction opposite the movement thereof caused by said birnetallicelement, said last-mentioned spring being eiective upon disengagement ofsaid element with said operating arm to cause disengagement of otherlatch arm with said tooth to permit movement of said drive means andengagement of said contacts, said switch arm mounted on said latchshaft, and a stop pin projecting from a face of said driving gear andengaging said support to cause said contacts to be locked in adisengaged position following a predetermined number of disengagementsand engagements of said contacts, said torsion spring being rewindableby rotation of said indicator arm.

2. A protective device for electrical apparatus comprising, a,stationary1v Contact,v a switch arm, rotatably Y, mounted-,on` a.rotatable shaft, one .end 'j of; said switch armtbeing a contact.endand the other end 101 saidswitch armhavng anelongated slot-therein,-a` rotatableescapement discV having a single tooththereonsaid1dischaving.

a pin'thereon projecting laterally therefrominto .saidv slot; rotation.`ofsaid disc causing vsaid .-contact endtof said switch armftoengage-anddisengagezsaid stationary contact, arvholding4 latch on-said `shafthavingl two-arms. each ,alternately engageable. with said toothvtao-hold -sadcontact end in an engaged and disengagedy position withrespect to said` stationary contact, arifactuating,Av arm on said shaftfor rotating said shaft to cause said latch-armste alternately engageand disengage said ftootha spring; and 'an' element `rel References-,oitatmta nie `0f this patent UNITED STATES Number f Number Nanie-"I-Datei"Y MacGahan`-` Jury# 1,-19192- Allutt Augsj- 219212 DaleyFeb?13.5"1934F=` Frarxkl Sept.-1, l1936?y Cooneyf Sept18-1v936ffHodnette" Jams," Y193'?-l Putman Dee. 3,"f 19'4o1* Putman-etais o't.65194221 Jonas Aug-r11, 19431` MayA May '23] 1944 smith Nv:v 251948smith: Dec.r `13;"1949-VSL FOREIGN-PATENTS .was

